For many years, hospital beds have had movable parts, such as an upper body support part movable between two positions in which it supports the patient in a sitting position and a prone position. Movement of these parts originally was effected manually by hospital personnel, for example by turning a crank provided on the bed.
As technology progressed, drive systems were incorporated into the beds to automatically effect movement of moveable parts. Although motors have been provided for a number of years to move such parts, the control circuits which operate the motors have changed. In recent years, some control circuits have been developed in which a microprocessor has the capability to control operation of one or more motors. While circuits of this type have been generally adequate for their intended purposes, they have not been satisfactory in all respects.
In particular, there have been concerns with safety, in that it is possible for a software error, static electricity, or an internal physical failure to cause the microprocessor to actuate its outputs in an erroneous manner. If such a failure happened to occur at a point in time when no hospital personnel were in the vicinity of the bed, the bed could move in a manner which caused serious injury to a patient. As an example, it will be recognized that a patient with a spinal injury could suffer serious permanent damage if a bed unexpectedly experienced a failure which caused it to move the patient from a prone position to a sitting position. Likewise, since many hospital beds have the capability to tilt the entire patient support surface, for example to place a patient in a position commonly referred to as a Trendelenburg position, erroneous movement of the bed to this position could result in the patient sliding off the bed onto the floor, with various types of bodily injury. While the likelihood of such problems is very small, it is nevertheless desirable to substantially eliminate them.
It is therefore an object of the present invention to provide a microprocessor-based bed control circuit which includes a fail-safe mechanism for preventing movement of any part of the bed unless an attendant is present.
It is a further object to provide such a control system which involves a minimal amount of additional hardware and cost in comparison to conventional microprocessor-based control systems.